1. Field of the Invention
The present invention relates generally to probe cards that are used to perform tests on semiconductor devices. The present invention more particularly relates to the cleaning of probe elements that extend from such probe cards.
2. Background Art
Individual semiconductor (integrated circuit) devices (dies) are typically produced by creating several identical dies on a semiconductor wafer, using known techniques of photolithography, deposition, and the like. Generally, these processes are intended to create a plurality of fully-functional integrated circuit devices, prior to singulating (severing) the individual dies from the semiconductor wafer. In practice, however, certain physical defects in the wafer itself and certain defects in the processing of the wafer inevitably lead to some of the dies being “good” (fully-functional) and some of the dies being “bad” (non-functional). It is generally desirable to be able to identify which of the plurality of dies on a wafer are good dies prior to their packaging, and preferably prior to their being singulated from the wafer. To this end, a wafer “tester” and “prober” in combination with a probe card may advantageously be employed to make a plurality of discrete pressure connections to a like plurality of discrete connection pads (bond or contact pads) on the dies. In this manner, the semiconductor dies can be tested and exercised, prior to singulating the dies from the wafer. A conventional component of a wafer test cell is a “probe card” to which a plurality of probe elements are connected, wherein the tips of the probe elements effect the pressure connections to the respective pads of the semiconductor dies.
More specifically, in the typical wafer testing process, the probe card is mounted to the prober, and probe elements (simply referred to as “probes”) extending from the probe card are brought into contact with pads formed on the dies of the wafer. Nonexclusive examples of such probes include elastic or springy contact probes (often referred to as “spring contacts” or “contact springs”), such as those disclosed in U.S. Pat. No. 6,184,053, entitled “Method of Making Microelectronic Spring Contact Elements,” U.S. Pat. No. 5,476,211, entitled “Method for Manufacturing Electrical Contacts, Using a Sacrificial Member,” U.S. Pat. No. 5,917,707, entitled “Flexible Contact Structure with an Electrically Conductive Shell,” U.S. Pat. No. 6,110,823, entitled “Method of Modifying the Thickness of a Plating on a Member by Creating a Temperature Gradient on the Member, Applications for Employing Such a Method, and Structures Resulting from Such a Method,” U.S. Pat. No. 6,255,126, entitled “Lithographic Contact Elements”, and PCT Publication No. WO 00/33089, entitled “Lithographic Contact Elements,” all of which are incorporated herein by reference.
In one process, an electrical connection between the prober and the pads is achieved by applying a predetermined pressure to the probes after the probes have been brought into contact with the pads so that the probes penetrate the material forming the surface of the pads and come into low-resistance contact with the portions forming the bodies of the pads. Upon contact and penetration of the pad material by the probe tips, the transfer of the pad material to the probe tips may contaminate the probe elements. The transferred contaminants may include the original pad material or an oxide of the pad material. It is possible that, depending on the transient operating conditions, the pad material may become alloyed (i.e., fused) to the probe tip material.
Alternatively, penetration of the pad surface material by the probe tips may produce debris (e.g., metallic chips) that is sometimes subsequently removed. Typically, elastic or springy probes are used to obtain a solid electrical connection between the prober and pads by compressing the probes with a predetermined pressure after the probes have been brought into contact with the pads. Once compressed, some contact technologies require that the probes are subjected to a slight X- and optionally Y-direction swipe, which causes a portion of the material forming the surface of the pads (e.g., a metallic oxide film) to be scraped off, thereby producing debris in the form of, for example, metallic “shavings” which may have an oxide film. This scraping movement across the pad surface also may produce “chips” of debris (e.g., metallic and/or oxide films) made of the material forming the surface of the pads. Even non-wiping contacts may become contaminated during probing, both by material transfer and/or alloying, as well as by adhering of loose particles of debris to the side of the probe element.
Foreign debris is not limited to only metal shavings and/or metal oxide chips, however, but may also include matter such as dust, polymeric or metallic oxide by-products resulting from the various process performed on wafers associated with the building of integrated circuits, or any other material that may interfere with obtaining a proper electrical connection between the probe tip and the die surface, or proper positioning of the probe itself in relation to the die. Various measures have been taken to prevent problems in achieving a satisfactory electrical contact between probes and pads, which include cleaning of the probe tips between die testing cycles.
In one conventional probe cleaning process, an abrading pad is used to remove foreign materials adhering to probes tips. The abrading pad can be composed of a mixture of an elastic base material and abrasive particles. Alternatively, the abrading pad can be composed of tungsten carbide. Foreign materials adhering to the tips of the probes are scraped off of the tips by repeating a cleaning cycle of pressing-and-extracting the tips of the probes against (and optionally into) the pad. The pressing-and-extracting cleaning cycle includes moving the abrading pad vertically (e.g., in the Z direction) against the probes, and then vertically away from the probes.
A disadvantage of the above described conventional cleaning process is that the portions of base material (e.g., silicone rubber) and/or abrasive particles (e.g., abrasive grains) may fall or chip off the abrading pad during the pressing-and-extracting process, thereby producing additional foreign material that may stick to the probe tips. Further, foreign matter (previously removed from probe) that has fallen onto the abrading pad may later stick to the probes being cleaned. Accordingly, additional cleaning steps may be necessary to acceptably clean the probes.
Additional steps may include blowing an organic solvent against the probes, and then blowing dry air against the probes. The use of such solvents is undesirable for many reasons. For example, the blowing of an organic solvent is time consuming and may be messy or hazardous. Additionally, blowing of dry air is time consuming. Further, special equipment is required to blow the solvents and the dry air. Fine brushes have also been used to clean probes.
Another attempt to improve upon the conventional probe cleaning process includes using a polymeric covered substrate to remove foreign materials following the pressing-and-extracting cleaning cycle described above. More specifically, a gel pad is positioned under the probes and then brought into contact with the probes, in a manner similar to the pressing-and-extracting used with the above-described abrading pad. Debris that has been loosened or produced by the abrading pad, therefore, sticks to the gel pad and is thereby removed from the probes. A disadvantage of this cleaning process is that an operator must typically swap the abrading pad with the gel pad during the cleaning process, because testing systems typically include only one auxiliary tray for holding such pads. This is undesirable because it prevents wafer testing from being a completely automated process, thereby significantly reducing wafer testing throughput.
Accordingly, there is a need for improved methods and apparatuses for cleaning probes.